1. Field of Endeavor
The present invention deals with the field of welding engineering. It relates to a method for joining two, in particular rotationally symmetrical, metal parts by a tungsten inert gas (TIG) welding process. The present invention also relates to a device useful for carrying out the method.
2. Brief Description of the Related Art
EP-A1-0 665 079 describes narrow-gap TIG welding for joining materials by a low-volume weld seam, this document focusing on the geometry of the seam. Here, the welding process is usually only monitored by direct visual inspection. Other users of narrow-gap TIG welding monitor the welding process using a video camera mounted externally on one side (outside the welding torch and outside the narrow gap). This affords only a restricted monitoring possibility, which limits the depth of the weld.
EP-A1-1 810 772 describes an inert gas supply for narrow-gap TIG welding, having a reduced quantity of inert gas in two streams of gas which protect the electrode and the entire guiding system. Here, monitoring in the direct vicinity of the arc is only possible visually. An increasing seam depth greatly restricts precise assessment of the seam quality. A fully automatic welding process is not described in this document and, indeed, cannot be implemented under these conditions. The method can be applied particularly effectively to the joining of rotationally symmetrical bodies in the construction of heavy machines such as, for example, rotors of turbomachines. Thick-walled components which are accessible only from one side, and therefore also cannot be welded on the root side, can also be effectively joined using the method described above.
A preferred field of application for the method is the joining of disks and hollow cylindrical forgings used for the construction of rotors for steam and gas turbines, compressors, and for turbo-generators. Such a rotor 20 is shown in FIG. 1. It is composed of a plurality of rotor disks 21, . . . , 25 which are integrally joined to one another by weld seams 26.
The workpiece parts which are to be joined and form a narrow gap may, however, also be welded with or without additional material at their butt joint by a base seam produced by electron-beam, plasma, laser-beam, or argon-arc welding processes. After the base seam, the further seam structure is often completed by submerged-arc welding. The method can be applied particularly effectively to the joining of rotationally symmetrical bodies in heavy machine construction. Thick-walled components which are accessible only from one side, and therefore cannot be rewelded on the root side, can also be effectively joined using the method according to DE-A1-26 33 829. The advantage of this method is that an inclusion-free, fine-grained structure is formed at the joint between the workpiece parts. There is no longer a primary structure either in the welded material or in the heat-affected zone. Subsequent normalizing or quenching and tempering are consequently unnecessary.
The welding process is not automated in any of these methods, and these methods all have the disadvantage that they do not have direct monitoring using one or more video systems directly in the welding nozzle, and therefore have to be monitored manually and do not allow automation for all applications.